A conventional integrated circuit (IC) device 10 shown in FIG. 1 typically houses a variety of "function" circuits (not shown), such as data buffers and power circuits, each receiving an input voltage from external circuitry (not shown) through one of multiple external pins 12. In general, the input voltage applied to each of the external pins 12 must be supplied within a limited range of voltages between maximum positive and negative rated voltages referred to as "over-stress" voltages. Otherwise, if the input voltage applied to one of the external pins 12 exceeds a maximum over-stress voltage, the function circuits (not shown) connected to the pin 12 may be damaged by voltage over-stress caused by excessive current flow or excessive voltage differentials within the function circuits (not shown). A positive over-stress voltage of 7.0 volts and a negative over-stress voltage of -1.0 volts are normal for a typical IC device 10 powered by a supply voltage of 5.0 volts.
When a customer returns a "defective" IC device to a manufacturer, the manufacturer may find it necessary or desirable to determine whether the "defect" in the returned device is a true defect or the result of the voltage over-stress described above. If the "defect" is a true defect caused by the manufacturing process, the manufacturer knows to adjust the process appropriately to reduce or eliminate the defect. However, if the "defect " is the result of voltage over-stress, the manufacturer knows there is no need to adjust the manufacturing process.
At the present time, manufacturers can only make educated guesses about the cause of a "defect" in an IC device, because no practical and definitive method exists to determine that an IC device has been damaged by voltage over-stress. If a manufacturer guesses wrong and incorrectly attributes a true defect to voltage over-stress, the manufacturer may fail to adjust the manufacturing process appropriately. As a result, the manufacturer may continue to manufacture defective IC devices without knowing it. While this would obviously be a problem in any industry, it is a particularly acute problem in the highly competitive IC device industry, where a slight difference in manufacturing yield between different manufacturers can be very significant. Therefore, there is a need in the art for an inventive device for definitively indicating that an IC device may have been subjected to an over-stressing input voltage.